TWI393495B - Electrical impedance precision control of signal transmission line for circuit board - Google Patents

Description

Characteristic impedance precision control structure of signal transmission circuit board

The invention relates to a characteristic impedance structure design of a flexible circuit board, in particular to a flexible circuit board structure design capable of controlling characteristic impedance precision of a circuit board or a flexible cable.

Most of the electronic devices have circuit boards or flexible cables to position various required circuit components, connector components, and the like. And transmit the signal to the required functional components. In the manufacturing technology of a circuit board, an extended signal transmission path is generally formed by a wiring technology on a substrate surface. Commonly used circuit board types are divided into hard circuit boards and flexible circuit boards or cables.

For example, the flexible cable used in various electronic products such as notebook computers, personal digital assistants, and mobile phones is generally constructed by juxtaposing a plurality of wires covered with an insulating layer in parallel to form a row of wires. The way in which the connector or circuit is soldered is used for the transmission of electronic signals.

Referring also to Figures 1 and 2, there are shown plan and cross-sectional views, respectively, of a conventional circuit board. The figure shows that a substrate 1 has a first surface 11 and a second surface 12. The substrate 1 extends in an extending direction to form a plurality of conductive contact ends 13 at the free ends of the substrate 1. The substrate 1 can be inserted into a slot 15 disposed in the circuit substrate 14 at its free end such that the respective conductive contact ends 13 of the substrate 1 are in contact with corresponding conductive contact ends in the socket 15.

On the first surface 11 of the substrate 1, a plurality of signal transmission paths 2 which may extend in parallel with each other and are spaced apart from each other are disposed. The respective signal transmission paths 2 disposed on the first surface 11 of the substrate 1 are spaced apart from each other by a predetermined interval d, and a plurality of wiring areas A1 and numbers covered by the signal transmission path 2 are defined on the first surface 11 of the substrate 1. Spacer A2 not covered by the signal transmission path 2. A cover insulating layer 3 is formed on the first surface 11 of the substrate 1 and covers the surface of each of the signal transmission paths 2 and the respective spacers A2. Finally, a conductive shielding layer 4 is formed on the surface of the cover insulating layer 3. The shielded conductive layer is generally grounded to the main ground path of the system to increase its shielding effect and form a ground plane of characteristic impedance.

Regardless of whether it is a hard circuit board or a flexible circuit board, since a plurality of signal transmission paths 2 are formed on the surface of the substrate 1, and the thickness of each of the signal transmission paths 2 is thin, the first surface 11 of the substrate 1 is covered. In the case of the insulating layer 3, the surface covering the insulating layer 3 never obtains a flat surface, but has a wavy concave-convex surface structure. Therefore, when the conductive shield layer 4 is formed on the surface of the insulating cover layer 3, a flat surface is never obtained on the surface of the conductive shield layer 4, and a wavy uneven surface structure as shown in Fig. 2 is also obtained.

Due to the above structural characteristics, the characteristic impedance (Electrical Impedance) of each signal transmission path on the circuit board is inconsistent, and it is difficult to control the accuracy of the characteristic impedance.

In practical applications, this board may cause problems such as poor impedance matching, signal reflection, electromagnetic wave divergence, loss of signal transmission and reception, and signal waveform distortion. These problems pose a great problem for boards that are currently commonly used in high-precision electronic devices.

Especially for electronic devices with higher operating frequencies (such as notebook computers), the higher the operating frequency, the higher the requirements for impedance accuracy. The circuit board structure made by the conventional technology cannot meet the needs of the industry. Especially for flexible circuit boards or flexible cables, because the material requirements are light and thin, and good flexibility is required, the insulating layer is usually laminated by a thin cover film. At this time, the uneven surface structure is more obvious, and the impedance precision is more Difficult to achieve.

Accordingly, it is an object of the present invention to provide a flexible circuit board structure that can control the characteristic impedance accuracy of a flexible circuit board, and in particular, a flexible circuit board or cable that requires thinness and flexibility.

Another object of the present invention is to provide a circuit board having a planarized insulating structure for fixing the distance between the transmission signal path and the conductive shielding layer and improving the characteristic impedance precision of the circuit board.

In order to achieve the above object, in the circuit board structure, at least a first planarization insulating layer is formed between a surface of the first cover insulating layer and the first conductive shielding layer, and the first planarization insulating layer is filled. The height difference between the surface of each of the first signal transmission paths and the interval between the respective first signal transmission paths is such that the characteristic impedance precision control of the flexible circuit board is achieved.

In terms of effects, the present invention provides a characteristic impedance precision control structure of a signal transmission circuit board. After each of the first signal transmission paths and the first cover insulating layer formed on the surface of the substrate, a flattening technique and structure are obtained. The surface does not have a wavy concave surface structure. Therefore, when the first conductive shielding layer is further formed on the surface of the first cover insulating layer, a flat first conductive shielding layer surface can be obtained. In this way, the characteristic impedance of each of the first signal transmission paths of the circuit board is controlled by a good characteristic impedance precision, without the impedance matching, signal reflection, electromagnetic wave divergence, loss of signal transmission and reception, signal waveform deformation, etc. in the prior art. problem.

Especially for the application of flexible circuit boards, if the flat material and thickness are selected properly and the suitable thin and light substrate is selected, the flexibility of the flexible circuit board can be increased, and the impedance precision can be greatly improved. For example, it can be improved from 100 Ω ± 15 Ω to 100 Ω ± 5 Ω before improvement, which is more practical.

In addition, in terms of structural characteristics, since each layer structure of the circuit board has a uniform flattening structure, when the material is thinner, the conductive shielding layer needs to be opened to improve the characteristic impedance value, especially when the silver paste is coated, the hole edge There is no problem of rendering (saw-tooth structure), which can reduce the influence of edge rendering on the impedance control value when opening, and thus achieve the purpose of impedance precision control.

The specific embodiments of the present invention will be further described by the following examples and the accompanying drawings.

Referring to Figure 3, there is shown a cross-sectional view of a first embodiment of the present invention. The figure shows that a substrate 1 has a first surface 11 and a second surface 12. On the first surface 11 of the substrate 1, a plurality of first signal transmission paths 2 extending parallel to each other and spaced apart from each other are disposed. The substrate 1 is a flexible substrate, and may be a rigid substrate or other type of substrate (such as a soft and hard bonding plate), and the substrate 1 may be one of a single-sided, double-sided or multi-layered board.

The first signal transmission path 2 is generally formed of a copper foil material or a composite material, and the cross section thereof may be a rectangle, a trapezoid, a circle, an ellipse or the like, but in practical terms, in terms of an etching process of the circuit board, It is mainly rectangular or trapezoidal. If an electronic cable is used, it may be rectangular or circular. And in the first signal transmission path 2, depending on different requirements, the signal transmitted by the first signal transmission path 2 is one of a differential mode signal or a common mode signal, and these There may be at least one grounded conductive path connected to the ground potential G at the periphery of the signal transmission path 2.

Each of the first signal transmission paths 2 is spaced apart from each other by a predetermined distance d. On the first surface 11 of the substrate 1, a plurality of routing areas A1 covered by the first signal transmission path 2 and a plurality of transmissions not transmitted by the first signal are defined. Space A2 covered by path 2.

A first cover insulating layer 3 is formed on the first surface 11 of the substrate 1 and covers the surface of each of the first signal transmission paths 2 and the respective spacers A2. The first cover insulating layer 3 is generally made of an insulating material, and may be one of a pure glue, a coverlay, and an ink.

The surface of the first cover insulating layer 3 has a first height h1 corresponding to the wiring area A1, and the surface of the first cover insulating layer 3 has a second height h2 corresponding to the space A2, the first height There is a height difference h between h1 and the second height h2.

In the structure of the present invention, the surface of the first cover insulating layer 3 is further formed with a first planarization insulating layer 5, and then a first conductive shielding layer 4 is formed on the surface of the first planarization insulating layer 5. The first planarization insulating layer 5 fills a height difference h between the first height h1 and the second height h2, so that the bottom surface of the first conductive shielding layer 4 corresponds to the wiring area A1 or corresponds to The spacers A2 each have substantially the same height. That is, in the structure of the present invention, a first planarization insulating layer 5 is further formed between the surface of the first cover insulating layer 3 and the first conductive shield layer 4. The material used for the first conductive shielding layer 4 is a silver material layer, and may also be an equivalent effect conductive layer, such as one of an aluminum material layer, a copper material layer, a conductive carbon paste, and a conductive particle glue layer.

The substrate 1, the first signal transmission path 2, the first cover insulating layer 3, the first planarization insulating layer 5, and the first conductive shielding layer 4 constitute a single-sided signal transmission circuit board 100.

The formation of the first planarization insulating layer 5 may be one of current conventional techniques such as ink printing, coating, roller coating, and the like. The material used for the first planarization insulating layer 5 may be an insulating material, a polymer material or the like. The preferred embodiment material used for the first planarization insulating layer 5 is formed by liquid printing, coating, roller coating curing, etc., formed on the surface of the first cover insulating layer 3, and then heated. The surface of the first cover insulating layer 3 is solidified by solid or ultraviolet irradiation. The first planarization insulating layer 5 may be formed on the entire surface of the first cover insulating layer 3, or may selectively form a partial first planarization insulating layer 5 in a local region where the characteristic impedance is required to be precise.

The first planarization insulating layer 5 is formed between the surface of the first cover insulating layer 3 and the first conductive shielding layer 4, so that the first conductive shielding layer 4 is formed to have a flat surface regardless of whether the top surface or the bottom surface is formed. Fully planar structure. Therefore, the first conductive shielding layer 4 forms a uniform height in the space A2 between the wiring area A1 and each of the first signal transmission paths 2 with respect to each of the first signal transmission paths 2, which means each of the first signals. The characteristic impedance between the transmission paths 2 is not different due to the difference in height, so that the purpose of the characteristic impedance precision control of the signal transmission circuit board, especially the flexible circuit board or the flexible wiring line can be achieved.

In practical applications, the signal transmitted by the first signal transmission path 2 has a good effect on the performance and reliability of the signal transmission, whether it is a differential mode signal or a common mode signal, because it needs to have a uniform characteristic impedance precision.

Referring to Figure 4, there is shown a cross-sectional view of a second embodiment of the present invention. The general structure of this embodiment is the same as that of the first embodiment, so the same components are labeled with the same component number, the difference is that the first conductive shielding layer 4 can be opened with different patterns of the opening structure 6 (see also the fifth The top view shown in the figure) can further adjust the characteristic impedance value of the first signal transmission path 2. The opening structure 6 can be a circular opening, a square opening, a diamond opening or other types. The opening structure can determine the size and regional distribution according to the characteristic impedance requirement to be adjusted.

Referring to Figure 6, there is shown a cross-sectional view of a third embodiment of the present invention. The general structure of this embodiment is the same as that of the first embodiment, except that two or more first planarizing insulating layers 51, 52 are formed between the surface of the first cover insulating layer 3 and the first conductive shield layer 4. The number of layers of the first planarization insulating layers 51, 52 may depend on the spacing between the respective first signal transmission paths 2, the choice of materials, the thickness of the first planarization insulating layer, and the effect. By forming the first planarization insulating layers 51, 52 on the surface of the first cover insulating layer 3 to achieve a more flat effect, more precise characteristic impedance precision control can be achieved.

Figure 7 is a cross-sectional view showing a fourth embodiment of the present invention. The general structure of this embodiment is the same as that of the first embodiment shown in FIG. 3, except that the second surface 12 of the substrate 1 is further formed with a second cover insulating layer 3a having unevenness and unevenness, and in the second cover insulating layer 3a. The bottom surface forms at least one second planarization insulating layer 5a, and a second conductive shielding layer 4a is formed on the bottom surface of the second planarization insulating layer 5a. That is, Fig. 7 shows an application example in which the technique of the present invention is applied to form a signal transmission path on one surface of a substrate. In practice, the second planarization insulating layer 5a may be formed directly on the second surface 12 of the substrate 1, and the second cover insulating layer 3a may be omitted.

Figure 8 is a cross-sectional view showing a fifth embodiment of the present invention. The general structure of this embodiment is the same as that of the fourth embodiment shown in FIG. 7, except that the second surface 12 of the substrate 1 is further provided with a plurality of second signal transmission paths 2a spaced apart from each other, and then sequentially formed second. The insulating layer 3a, the second planarizing insulating layer 5a, and the second conductive shielding layer 4a are covered. That is, Fig. 8 shows an application example in which the technique of the present invention is applied to form a signal transmission path on both surfaces of a substrate.

The substrate 1, the first signal transmission path 2, the first cover insulating layer 3, the first planarization insulating layer 5, the first conductive shielding layer 4, the second signal transmission path 2a, the second cover insulating layer 3a, and the second conductive shield The layer 4a and the second planarization insulating layer 5a constitute a double-sided signal transmission circuit board 200.

Figure 9 is a cross-sectional view showing a sixth embodiment of the present invention. This embodiment constitutes a multi-layered signal transmission circuit board based on the structure of the embodiment shown in FIG. For example, the two-layer stacked structure shown in the figure includes a substrate 1, a first signal transmission path 2, a first cover insulating layer 3, a first conductive shielding layer 4, and a first signal transmission circuit board 100a. A planarization insulating layer 5, a second cladding insulating layer 3a, a second conductive shielding layer 4a, and a second planarization insulating layer 5a. Similarly, the second signal transmission circuit board 100b also includes a substrate 1, a first signal transmission path 2, a first cover insulating layer 3, a first conductive shielding layer 4, a first planarization insulating layer 5, and a second cover insulating layer. 3a, a second conductive shielding layer 4a, and a second planarization insulating layer 5a. After the first signal transmission circuit board 100a and the second signal transmission circuit board 100b are stacked on top of each other, a multi-layered signal transmission circuit board having a characteristic impedance precision control structure can be constructed. The first signal transmission circuit board 100a and the second signal transmission circuit board 100b form a laminated structure 300.

In the industrial application of the present invention, a plurality of stacked structures can be combined. E.g:

1. Stacking at least two of the single-sided signal transmission circuit boards to form a stacked structure of a plurality of single-sided signal transmission circuit boards.

2. Stacking at least two of the double-sided signal transmission circuit boards to form a stacked structure of a plurality of double-sided signal transmission circuit boards.

3. Stacking at least one of the single-sided signal transmission circuit boards and at least one of the double-sided signal transmission circuit boards to form a composite stacked structure.

The above embodiments are merely illustrative of the structural design of the present invention and are not intended to limit the present invention. Any modifications and variations of the above-described embodiments can be made by those skilled in the art, and such changes are still within the spirit of the invention and the scope of the invention as defined below. Therefore, the scope of protection of the present invention should be as set forth in the appended claims.

1. . . Substrate

11. . . First surface

12. . . Second surface

2. . . First signal transmission path

3. . . First cover insulating layer

4. . . First conductive shielding layer

5, 51, 52. . . First planarization insulating layer

2a. . . Second signal transmission path

3a. . . Second cover insulating layer

4a. . . Second conductive shielding layer

5a. . . Second planarization insulating layer

6. . . Opening structure

100. . . Single-sided signal transmission board

100a. . . First signal transmission board

100b. . . Second signal transmission circuit board

200. . . Double-sided signal transmission board

300. . . Stacked structure

A1. . . Wiring area

A2. . . Spacer

d. . . spacing

G. . . Ground potential

H1. . . First height

H2. . . Second height

h. . . Height difference

Figure 1 shows a schematic diagram of a conventional flexible circuit board;

Figure 2 is a cross-sectional view showing the section 2-2 in Figure 1;

Figure 3 is a cross-sectional view showing a first embodiment of the present invention;

Figure 4 is a cross-sectional view showing a second embodiment of the present invention;

Figure 5 is a top plan view showing a second embodiment of the present invention shown in Figure 4;

Figure 6 is a cross-sectional view showing a third embodiment of the present invention;

Figure 7 is a cross-sectional view showing a fourth embodiment of the present invention;

Figure 8 is a cross-sectional view showing a fifth embodiment of the present invention;

Figure 9 is a cross-sectional view showing a sixth embodiment of the present invention.

100. . . Single-sided signal transmission board

1. . . Substrate

11. . . First surface

12. . . Second surface

2. . . First signal transmission path

3. . . First cover insulating layer

4. . . First conductive shielding layer

5. . . First planarization insulating layer

A1. . . Wiring area

A2. . . Spacer

d. . . spacing

G. . . Ground potential

H1. . . First height

H2. . . Second height

h. . . Height difference

Claims (15)

A characteristic impedance precision control structure for a signal transmission circuit board includes: a substrate having a first surface and a second surface; a plurality of first signal transmission paths extending on the first surface of the substrate, each The first signal transmission paths are spaced apart from each other by a predetermined interval, and a plurality of wiring regions covered by the first signal transmission path and a plurality of spacer regions not covered by the first signal transmission path are defined on the first surface of the substrate; a first cover insulating layer formed on the first surface of the substrate and covering the surface of each of the first signal transmission paths and the respective spacer regions, the surface of the first cover insulating layer having the first portion corresponding to the wiring region a height, and a surface of the first cover insulating layer has a second height corresponding to the spacer, and a height difference exists between the first height and the second height; a first conductive shielding layer is located at the height a surface of the insulating layer; the first surface of the first insulating layer and the first conductive shielding layer are formed with at least one first planarizing insulating layer, the first The canalization insulating layer fills the height difference, so that the first conductive shielding layer has substantially the same height regardless of the wiring area corresponding to the substrate or the spacing area corresponding to the substrate, and the substrate and the first signal transmission The path, the first cover insulating layer, the first planarization insulating layer, and the first conductive shielding layer form a single-sided signal transmission circuit board. The characteristic impedance precision control structure of the signal transmission circuit board according to claim 1, wherein the first conductive shielding layer is a silver material layer, an aluminum material layer, a copper material layer, and a conductive carbon paste (Carbon) ), one of the conductive particle glue layers. The characteristic impedance precision control structure of the signal transmission circuit board of claim 1, wherein the first conductive shielding layer is a full planar structure. The characteristic impedance precision control structure of the signal transmission circuit board of claim 1, wherein the first conductive shielding layer comprises a plurality of opening structures. The characteristic impedance precision control structure of the signal transmission circuit board according to claim 1, wherein the signal transmission line has one of a rectangular, a trapezoidal shape, a circular shape and an elliptical shape. The characteristic impedance precision control structure of the signal transmission circuit board of claim 1, wherein the signal transmitted by each of the first signal transmission paths is one of a differential mode signal or a common mode signal. The characteristic impedance precision control structure of the signal transmission circuit board according to claim 1, wherein the first planarization insulating layer is formed by one of ink printing, coating, and roller coating. The characteristic impedance precision control structure of the signal transmission circuit board according to claim 1, wherein the cover insulating layer is one of a thin film, a pure glue or an insulating ink. The characteristic impedance precision control structure of the signal transmission circuit board according to claim 1, wherein the substrate is one of a flexible substrate and a hard substrate. The characteristic impedance precision control structure of the signal transmission circuit board of claim 1, further comprising: at least one second planarization insulating layer formed on the second surface of the substrate; and a second conductive shielding layer formed On the surface of the second planarization insulating layer. The characteristic impedance precision control structure of the signal transmission circuit board of claim 10, wherein the second planarization insulating layer further comprises a second cover insulating layer between the second surface of the substrate. The at least two of the single-sided signal transmission circuit boards are stacked to form a plurality of single-sided signal transmission circuit boards, as described in the characteristic impedance precision control structure of the signal transmission circuit board of claim 1 structure. The single-sided signal transmission circuit board further includes: a plurality of extended second signal transmission paths disposed on the second surface of the substrate, wherein the characteristic signal impedance control structure of the signal transmission circuit board of claim 1 is further included Each of the second signal transmission paths is spaced apart from each other by a predetermined interval, and a plurality of wiring regions covered by the second signal transmission path and a plurality of spacer regions not covered by the second signal transmission path are defined on the second surface of the substrate. a second cover insulating layer formed on the second surface of the substrate and covering the surface of each of the second signal transmission paths and the respective spacers, the second cover insulating layer having the first portion corresponding to the wiring region a height, and the second cover insulating layer has a second height corresponding to the spacer, a height difference exists between the first height and the second height; at least one second planarization insulating layer is formed at the height Covering the surface of the insulating layer; a second conductive shielding layer on the surface of the second planarizing insulating layer; wherein the substrate, the second signal transmission path, and the second covering The edge layer, the second planarization insulating layer, the second conductive shielding layer, the first signal transmission path, the first cover insulating layer, the first planarization insulating layer, and the first conductive shielding layer form a double-sided layer Signal transmission board. The characteristic impedance precision control structure of the signal transmission circuit board according to claim 13 of the patent application, wherein at least two of the double-sided signal transmission circuit boards are stacked to form a stack of a plurality of double-sided signal transmission circuit boards structure. According to the characteristic impedance precision control structure of the signal transmission circuit board of claim 13, at least one of the single-sided signal transmission circuit boards and at least one of the double-sided signal transmission circuit boards are stacked to form a stacked structure.